Developmental Logic as Circuit Blueprint.

Author

Jelly Soffers

Overview

This tutorial guides you through the Neuroglancer interface to examine the escape circuit.

First, you will first visualize the key neurons of this survival response. The giant fiber neurons that descend from the brain into the ventral nerve cord relay the sensory input that detects a looming stimulus, and relays it to the motor neurons that trigger the jump response. These motorneurons are called the tergotrochanteral motor neurons (TTMn’s), after the tergotrochanter muscle they innervate, which is a leg extensor muscle.

Follow this link to look at the brain, and see the location of the cell bodies of the giant fiber neurons.

Next, you will investigate how neurons populations derived from different stem cells interact with these same motor neurons contribute to premotor control of the tergotrochanteral motor neuron (TTMn)

Overview of Dataset (for reference)

Presynaptic partners of the TTMn were identified from the MANC connectome v1.2 using a neuPrint query that extracts upstream neurons forming ≥10 synapses onto the TTMn. Neurons not assigned to a hemilineage were excluded from analysis. The resulting dataset is provided in Table 1, which includes neuron IDs, hemilineage identity, synapse counts, and neurotransmitter annotations.

Figure 1: click to open Neuprint link or scan the QR code.

This link directs you to a viewer screen, which has a few items preloaded:

  • The full EM volume as a structural reference;
  • Neuropil outlines for anatomical context;
  • The Giant Fiber (from the neck into the ventral nerve cord, the central brain is chopped off);
  • The jump muscle motor neuron (TTMn);
  • Neurons from specific neuronal populations (hemilineages) that synapse with the TTMn (AKA: TTMn premotor input);
  • The complete hemilineage as reference (for thoracic segment 2).
(a) cartoon of the escape circuit
(b) weigthed connectity graph per hemilineage
(c) 3D screenshot of giant fiber- TTMn interface
(d) 3D screenshot with hemilineage07B added
Figure 2: Giant Fiber

Classroom Execution

A. Orientation in Neuroglancer

  1. Open the Neuroglancer link (see Figure 3 (a)).
  2. Identify the following elements: Left panel 1
    • TTMn (motor neuron; typically highlighted in orange)
    • GF neuron (command neuron; typically highlighted in blue)
    • Neuropil boundaries, focusing on the T2 neuromere
    • Premotor input neurons (loaded from the query dataset)
    • Hemilineage reference neurons (to evaluate the proportion of a hemilineage that synapses to the TTMn)
  3. Adjust visualization settings:
    • Left window, eye icon: Toggle layers on/off to isolate specific neuron populations (see Figure 3 (b), Figure 3 (c)).
    • Right window, Use transparency controls to visualize spatial overlap (see Figure 3 (d))
    • Rotate to a dorsal view for consistency with Figure 3

B. Identifying Premotor Inputs

  1. Select individual hemilineage neurons from the dataset layer.
  2. Trace their projections relative to:
    • The TTMn dendritic field
    • The GF axon
  3. Use view toggles to:
    • Highlight synaptic contacts onto the TTMn
    • Compare morphology across neurons from different hemilineages

C. Guided Analysis (connect to main text questions)

Using the Neuroglancer view and dataset, address the following:

  • Which hemilineages provide the strongest synaptic input to the TTMn?
  • Does hemilineage 7B form direct synaptic contacts with the TTMn? Where are these located?
  • Do neurons from the same hemilineage show similar or diverse morphologies?
  • How are inputs spatially organized relative to the TTMn dendrites?
  • Based on neurotransmitter identity, which hemilineages are likely excitatory vs. inhibitory? Tip:
    • Acetylcholine (ACh) → excitatory
    • Glutamate (Glu) → often excitatory
    • GABA → inhibitory?
  • How might these chemical inputs interact with the fast electrical GF→TTMn pathway?

D. Linking Structure to Hemilineage Identity (Advanced)

  1. Cross-reference selected neurons with Table 1:
    • Identify their hemilineage assignment
    • Note synapse counts onto TTMn
    • Record neurotransmitter identity
  2. For each hemilineage:
    • Determine how many neurons contribute input to the TTMn
    • Estimate their relative contribution to total TTMn input
(a) Layer control
(b)
(c)
(d) Render tab
(e) Segmentation tab
Figure 3: Neuroglancer

Hemilineage

Table 1: Hemilineage
Hemilineage Row Labels Sum of c.weight
17A 11404 10
08A 22549 12
169711 10
00A 16388 15
17047 12
12B 29239 33
06B 10812 18
11682 18
16B 14424 59
(blank) 10000 146
10634 13
24797 10
225692 12
13B 11111 161
35435 17
156615 10
07B 14155 59
16174 34
16544 45
18516 23
20588 47
101550 40
20A.22A 11530 86
11877 102
13081 58
16156 10
04B 15036 58
16171 13
16530 23
16640 31
16772 26
19473 35
21464 14
22299 21
101891 37
18B 13645 26
13846 156
14882 22
17245 21
17824 10
18131 14
21171 22
21A 15336 75
16186 97
16427 12
17013 139
17073 167
17558 30
18306 11
20731 59
20905 64
24383 13
27296 23
28678 11
36932 21
101974 28
152381 95
13A 14366 256
15024 178
16681 90
17350 183
27506 14
33275 136
Grand Total 3291